A multi-mission spacecraft bus structure is provided which has a plurality of internal thermally-isolated cells, and a plurality of external mounting surfaces The spacecraft bus structure comprises a plurality of half frame panels, which are secured to plurality of longerons. The half-frame panels each have a pair of broad planar surfaces, a center abutting surface, a pair of end-abutting surfaces, and a pair of miter joint surfaces. Adjacent half-frame panels can either join at the center abutting surfaces, or at the edge mounting surfaces The bus structure is further sealed at the top and at the bottom by mounting plates. External electrical equipment bays can be secured to a plurality of the external mounting surfaces. Externally mounted radiators are provided to remove excess heat from the internal cells. The radiators each face in directions distinct from each other.